The present invention relates to an electrical transmission arrangement for use preferably within the microwave field, in particular a microstrip arrangement or a strip-line arrangement. The invention is primarily intended to be used in a connection where there is need to transfer electrical signals between different layers of a dielectric substrate in a circuit card.
In the transmission of electrical signals in the microwave field, especially in circuit cards, it is usual to make use of the microstrip technology or strip-line technology. In microstrip technology, a usually flat conductor is used, separated from an associated ground plane of a dielectric substrate, where the dielectric substrate is frequently the carrier of a circuit card. The ground plane is also usually flat and mainly arranged in parallel with and separate from the conductor at an essentially constant distance. The strip-line technology comprises the same components as the microstrip technology, but with a second ground plane arranged on the opposite side of the conductor, with respect to the first ground plane. The second ground plane should also be arranged mainly in parallel with the conductor, separated from the conductor by the dielectric substrate at an essentially constant distance, preferably at the same distance as the first ground plane.
As can be seen from the above description, the conductor in the arrangements which are constructed in microstrip or strip-line have their main extension in two planes since the conductors are flat. The result is that problems can arise if it is intended to use such arrangements to transmit electrical energy in other directions than the two directions which are defined by the planes of the conductor.
The requirement for transmitting electrical energy in other directions than those which are defined by the planes of the conductor can arise, for example, in circuit cards which are constructed in so-called multilayer technology. As is indicated by the name, the multilayer technology means that conductors and other components are arranged in different layers in a dielectric substrate which forms the carrier for a circuit card. There may also be a requirement for transmitting signals from components or conductors on one of the layers of the circuit card to conductors or components on another one of the layers of the circuit card.
Another example for a case, where there can be a requirement for transmitting signals from a strip-line arrangement or microstrip arrangement in a direction which deviates from the directions which are defined by the planes of the conductor is if one wishes to connect one circuit or one conductor in one layer in the circuit card with a contact which is situated in connection with one of the surfaces of the circuit card.
A conceivable way of connecting two strip-line conductors or microstrip conductors in different layers in a multilayer circuit card is to introduce a connection between the conductors. Such a connection between conductors in two different layers, however, will be affected by power losses which increase with the length of the connection which limits the possibility for using this type of connections. One of the factors which cause the power losses is that a connection which goes in a direction which deviates from the planes which are defined by the conductors will cause mismatching of the impedance of the circuit.
Document GB 2 272 112 A shows an arrangement with connections between different layers of microstrip conductors in a multilayer circuit card. For reasons set forth above, the connection which is shown in this arrangement exhibits limitations with respect to the maximum distance between two conductors which are to be connected.
The problem which is solved by the present invention is such that, with low power losses and distances which are largely optional, electrical signals can be transferred between conductors and components in different layers in a multilayer circuit card, in particular if the conductors and components which will be connected to one another are constructed in microstrip technology or strip-line technology.
In microstrip applications, this problem is solved with the aid of an electrical transmission arrangement which comprises a first section of a conductor with a main extension in two planes, a first section of a ground plane which extends essentially in parallel with the conductor section on the first side of the conductor section, at a certain distance and has a main extension in the same two planes as the conductor section. The transmission arrangement also comprises at least one second and one third section of the said conductor, which sections have their main extensions in the same two planes as the first section of the conductor, the second conductor section being displaced in parallel with respect to the first conductor section, and the third conductor section being displaced in parallel with respect to the second conductor section.
The transmission arrangement according to the invention also comprises at least one second and one third section of the said ground plane, which sections have their main extensions in the same two planes as the first section of the ground plane, the second ground plane section being displaced in parallel with respect to the first ground plane section, and the third ground plane section being displaced in parallel with respect to the second ground plane section
The parallel displacements of conductor sections and ground plane sections are done in a direction which is at right angles to the two planes which define the main extensions of the conductor sections and ground plane sections, each conductor section being electrically connected at least to the closest of the second conductor sections, each ground plane section being electrically connected at least to the closest of the second first plane sections. The conductor sections being separated from the ground plane sections by a dielectric material.
The connection between two adjacent conductor sections is suitably situated in connection with the edges of the two conductor sections which are closest to one another.
In a particularly preferred embodiment of the invention, the conductor sections are also progressively displaced with respect to one another in a direction which coincides with one of the two planes which define the main extensions of the conductor sections, and the ground plane sections are also progressively displaced with respect to one another in one direction which coincides with one of the two planes which define the main extensions of the ground plane sections.
To facilitate the construction of a transmission arrangement according to the invention, two adjacent ground plane sections can be given different lengths in the direction in which they are progressively displaced with respect to one another, whereby the displacement of the ground plane sections is produced by one part of a ground plane section extending past an adjacent ground plane section.
To minimize the power losses in a transmission arrangement according to the invention, the ground plane sections and conductor sections should be constructed in such a manner that all points on all conductor sections have essentially the same capacitance with respect to the ground plane. This is suitably done by the connection between two adjacent conductor sections passing at least one edge in a ground plane section, which edge is constructed for impedance matching. In a preferred embodiment of the invention, this construction provides at least a part of the edge with an elliptical shape.
If the transmission arrangement according to the invention is to be used in association with a strip-line, one further ground plane section should also be arranged on the other side of at least one of the conductor sections, and this ground plane section is also separated from the conductor section by a dielectric material. The further ground plane section is suitably, but not necessarily, situated at the same distance from the conductor section as the ground plane section which is situated on the first side of the conductor section.
In association with a strip-line, the transmission arrangement can also comprise furthermore at least two ground plane sections situated on the second side of the corresponding conductor section, separated from their corresponding conductor sections by a dielectric. material, whereby the ground plane section on both sides of a conductor section are situated at essentially the same distance from the conductor section, separated from the conductor section by a dielectric material. More generally, each ground plane section on the said second side of a conductor section can quite simply correspond to a ground plane section on the first side of the conductor section, taking into account the rule of equal distances between conductor and ground plane on both sides of the conductor.
As in the embodiments of the invention described earlier, two adjacent ground plane sections on the second side of a conductor section can exhibit different lengths in the direction in which the conductor sections are progressively displaced with respect to one another.
The ground plane sections in the embodiment of the invention which is intended for strip-line applications essentially have the same construction for impedance matching as the ground planes on the first side of the conductor sections, which has been described above.